I’m trying to strike a festive note this week, but what am I to do about the needs of a seasonally oblivious bunch of readers? Recent emails range from: “Should I cut down or leave standing a new and stunning Salvia 'Amistad’ that flowered all summer?” (hold off on this one, Diana Blake, leave the top growth as protection from extreme weather and don’t cut it back until March), to a request for suggestions regarding invasive weeds in between elderly block paving. (There is no rush on this one, David Woolf, so I will address it in the New Year, when Gardening goes back to being free range and Thorny Problems plumps up again).

So, with a nifty nudge to get you all into the obligatory Yuletide mood (yes, readers, you do detect a weary note of Bah Humbug, here), I will answer a couple of seasonally appropriate questions often asked about holly and ivy.

Holly unberried

I have a pair of small standard holly trees in tubs. Why do they never carry any berries?

This one is possibly all about sex. Only female English holly bushes (Ilex aquifolia) bear berries, and they need a male “mate” somewhere in the vicinity — in the next-door garden, for instance – for pollination to take place: maybe yours are simply the same sex.

More likely, is that your standard holly trees are being pruned at just the wrong time of year, in summer. Flowers and subsequent berries are produced on the previous year’s growth, so you need to prune them just once every couple of years or so, very early in the growing season, for the trees to perform in the berry department.

This is a bit of a tall order with standard holly trees whose outlines need to be kept crisp by routine snippery – easier perhaps with regular trees or even hedges, about which the maintenance can be a little more lax. There is a bit more to it, however. Summer drought occasionally stops hollies from berrying up satisfactorily, and young hollies, of course, may not do much for five years or so.

And, back to the sex thing, don’t be fooled by labels: 'Golden King’ is, despite its name, a female hybrid, while its natural partner 'Golden Queen’ is – you guessed it – male.

However, there are some boring hollies that don’t even bother to flower at all – as well as a few that, being self-fertile, can do it all by themselves, the most reliable of which is one with a distinctly androgynous name, Ilex 'J C van Tol’.

Puzzling habits of ivy

Why does some ivy climb, flower and produce berries, while some just seems to run around being a nuisance on the ground?

Ivy is a natural climber, using its aerial (clinging) roots to shinny up any vertical surface it can find. It seems to drive most gardeners to distraction when it is in its invasive mode, running around the ground looking for something to climb. Once up aloft, it changes completely in character, sending out cantilevering wiry branches that produce clusters of rather greenish flowers that are highly attractive to pollinating insects.

In early autumn you can see and hear them at it: massed wasps, honey bees, hoverflies and even a few late-summer butterflies having a ball. Around this time of year the flowers have turned into greenish berries, eventually blackening as they ripen, beloved by robins and wrens in late winter.

Ivy is, therefore, a highly decorative plant, valuable to wildlife for the shelter and food it provides. But it has got itself a terrible reputation by running amok on the ground when it can’t find anything to climb, and when in arborescent mode, potentially damaging dodgy mortar in old walls and rendering deciduous old trees on their last legs top-heavy in high winds. Rather a shame, I feel.

Santa-friendly boots

Just as I finished writing this, an email pinged in from an apparently avid reader from abroad (FC), asking me to recommend a pair of really warm boots for him to wear on a worldwide wintry journey upon which he is shortly to embark. With the ice cap melting and so much snow turning to slush, he says, he now needs boots that will keep his toes not just toasty but really dry as well, replacing at last the baggy old leaky old ones he has worn for years and years.

The Original Muck Boot Company (01335 372600; Belstane) gets my vote this year, FC – and they will, I think, look extremely fetching with your bright red, fur-trimmed overcoat. I bet you didn’t see that one coming.

Thorny problem? Write to Thorny Problems at helen.yemm@telegraph.co.uk or Gardening, The Daily Telegraph, 111 Buckingham Palace Road, London SW1W 0DT. Helen Yemm can answer questions only through this column